1. Field of the Invention
The present invention relates to a diode-pumped solid-state laser device and a manufacturing method of the same.
2. Description of the Related Prior Art
For a diode-pumped solid-state laser device to obtain a laser beam of a high beam quality at a high output, it is necessary to achieve a homogeneous distribution of pumping light within a laser rod across the cross section of the rod. For example, when the distribution of pumping light within the laser rod makes a profile with the center of the rod being higher, the thermal lensing effect in the laser rod becomes greater, which raises problems, such as saturation of a laser output, deterioration in the quality of a laser beam profile, and damage in the laser rod. Conventionally, the optical diffusing and condensing method has been proposed in order to achieve a homogenous pumping distribution within the laser rod.
FIG. 1 shows a cross section of a conventional diode-pumped solid-state laser device. A cooling tube 3 is placed outside a laser rod 1. Cooling water 6 flows through a space between the laser rod 1 and the cooling tube 3, and directly cools the laser rod 1 and a rod holder. Pumping laser diodes (hereinafter, abbreviated to LDs) 2 are placed outside the cooling tube 3, and side-pump the laser rod 1 through antireflection coating 17. An optical diffusing reflector 15 is provided outside to come in close contact with the cooling tube 3. The optical diffusing reflector 15 is made of a material, such as ceramic, and the surface coming in close contact with the cooling tube 3 is made rough to form a diffusing reflection mirror. The diffusing reflection mirror reflects LD light 13 randomly to be absorbed homogeneously into the laser rod 1.
However, because the LD light 13 heats the optical diffusing reflector 15, there arises a problem that heat damages the diffusing reflection mirror. In order to prevent damage on the diffusing reflection mirror, the optical diffusing reflector 15 has to be cooled by cooling water which is fed through holes. The optical diffusing reflector 15, however, increases in thickness due to the need to provide the cooling holes, which in turn increases a distance between the pumping LDs 2 and the laser rod 1. It is therefore necessary to provide lenses 16 to make the LD light 13 focus to the laser rod 1 efficiently. As has been described, the conventional method has a problem that costs are increased and the fabrication becomes complicated due to plural components, such as the optical diffusing reflector, the condenser lenses, a holding mechanism and a cooling mechanism of the optical diffusing reflector.
There has been disclosed a diode-pumped solid-state laser device configured to include, instead of the optical diffusing reflector, a cylindrical member provided outside and coaxially with the cooling tube and having a high reflection coating on the inner surface and pumping LD light-introducing slits on the side surface, so that pumping LD light is reflected on the reflection coating on the inner surface of the cylindrical member (see, for example, Japanese Laid-Open Patent Application No. 2001-244526).
With the technique disclosed in the aforementioned publication, however, a patterned reflection coating has to be provided on the inner surface of the cylindrical member which is a difficult fabricating method. Moreover, it is necessary to adjust in such a manner that pumping LD light that goes incident on the cylindrical member will be reflected on the reflection coating on the inner surface of the cylindrical member and returned to the incident position again (referred to as the condition for direct reflection in the aforementioned publication), which makes it quite difficult to align the pumping LDs. For the reasons described above, the diode-pumped solid-state laser device manufactured with the use of the disclosed technique has a drawback that the costs are increased as a matter of course.